Today in spite of the fact that resources (like CPU power and disk space) are cheaper than before, increasing e-mail usage and the unpredictability associated with its size and volume can be very costly to individuals and corporations alike. E-mail is now a very commonly used way of sending and receiving information. E-mail may be sent between users on a local area network or a wide area network across the Internet for example. E-mail usage continues to increase, and it is not uncommon for an e-mail user to receive many hundreds of messages in a day. Many of these messages may themselves have lengthy attachments which need a great deal of storage space, such as graphics files. In addition, there is growth in volume of spam mail which is unsolicited (predominantly unwanted) e-mail, and which also serves to fill up a user's mailbox. When a mailbox runs out of user space to store incoming mail, existing e-mail systems simply then bounce the mail back to the sender indicating that this mail was not delivered. There is, however, no way that the receiver knows that a mail delivery failed. Thus, an important e-mail could be missed, and the receiver does not know this. This could have potentially disastrous consequences in business for example. In cases where the mail sent is large in size (perhaps due to attachments) the e-mail software does not deliver mail if the user space available is less than the mail size even if the amount of user space available is substantial.